Compaction of railroad ballast is well known. Compaction causes the irregularly-shaped pieces of ballast to vibrate into position against each other and the cross ties. Thus the ballast fits more tightly than when simply unloaded onto the track by gravity flow. Tamping seeks to compact the ballast beneath the sleepers to provide a more stable track and reduce settling of the track due to traffic.
Conventional tampers have utilized pivotally mounted tamping tools which attempt to squeeze the ballast inwardly beneath the ties as the tools pivot about a horizontal axis. It is clear from elementary geometry that such devices can thus only provide such compaction as may be accomplished in the arc swept by the tools, thus very little tamping may actually occur beneath the cross tie.